In the applied sciences, various fields of study require the analysis of two-dimensional (2-D) or three-dimensional (3-D) volume data sets wherein each data set may have multiple attributes representing different physical properties. An attribute, sometimes referred to as a data value, represents a particular physical property of an object within a defined 2-D or 3-D space. A data value may, for instance, be an 8-byte data word which includes 256 possible values. The location of an attribute is represented by (x, y, data value) or (x, y, z, data value). If the attribute represents pressure at a particular location, then the attribute location may be expressed as (x, y, z, pressure).
In the medical field, a computerized axial topography (CAT) scanner or magnetic resonance imaging (MRI) device is used to produce a picture or diagnostic image of some specific area of a person's body, typically representing the coordinate and a determined attribute. Normally, each attribute within a predetermined location must be imaged separate and apart from another attribute. For example, one attribute representing temperature at a predetermined location is typically imaged separate from another attribute representing pressure at the same location. Thus, the diagnosis of a particular condition based upon these attributes is limited by the ability to display a single attribute at a predetermined location.
In the field of earth sciences, seismic sounding is used for exploring the subterranean geology of an earth formation. An underground explosion excites seismic waves, similar to low-frequency sound waves that travel below the surface of the earth and are detected by seismographs. The seismographs record the time of arrival of seismic waves, both direct and reflected waves. Knowing the time and place of the explosion the time of travel of the waves through the interior can be calculated and used to measure the velocity of the waves in the interior. A similar technique can be used for offshore oil and gas exploration. In offshore exploration, a ship tows a sound source and underwater hydrophones. Low frequency, (e.g., 50 Hz) sound waves are generated by, for example, a pneumatic device that works like a balloon burst. The sounds bounce off rock layers below the sea floor and are picked up by the hydrophones. In either application, subsurface sedimentary structures that trap oil, such as faults and domes are mapped by the reflective waves.
The data is collected and processed to produce 3-D volume data sets. A 3-D volume data set is made up of “voxels” or volume elements having x, y, z coordinates. Each voxel represents a numeric data value (attribute) associated with some measured or calculated physical property at a particular location. Examples of geological data values include amplitude, phase, frequency, and semblance. Different data values are stored in different 3-D volume data sets, wherein each 3-D volume data set represents a different data value. In order to analyze certain geological structures referred to as “events,” information from different 3-D volume data sets must be separately imaged in order to analyze the event.
Certain techniques have been developed in this field, however, for imaging multiple 3-D volume data sets in a single display. One example includes the technique published in The Leading Edge called “Constructing Faults from Seed Picks by Voxel Tracking” by Jack Lees. This technique combines two 3-D volume data sets in a single display, thereby restricting each original 256-value attribute to 128 values of the full 256-value range. Another conventional method combines the display of two 3-D volume data sets, containing two different attributes, by making some data values more transparent than others. This technique becomes untenable when more than two attributes are combined.
Other, more advanced, techniques used to combine two different 3-D volume data sets in the same image are illustrated in U.S. patent application Ser. No. 09/936,780 and Ser. No. 10/628,781 assigned to Magic Earth, Inc. and incorporated herein by reference.
The '780 application describes a technique for combining a first 3-D volume data set representing a first attribute and a second 3-D volume data set representing a second attribute in a single enhanced 3-D volume data set by comparing each of the first and second attribute data values with a preselected data value range or criteria. For each data value where the criteria are met, a first selected data value is inserted at a position corresponding with the respective data value in the enhanced 3-D volume data set. For each data value where the criteria are not met, a second selected data value is inserted at a position corresponding with the respective data value in the enhanced 3-D volume data set. The first selected data value may be related to the first attribute and the second selected data value may be related to the second attribute. The resulting image is an enhanced 3-D volume data set comprising a combination of the original first 3-D volume data set and the second 3-D volume data set. The '780 application also describes a technique for displaying an enhanced 3-D volume data set related to one of a plurality of attributes by selecting attribute data values within a predetermined data value range and inserting a preselected data value at a position corresponding with the data value in the enhanced 3-D volume data set when the data value is within the data value range, or inserting another preselected data value at a position corresponding with the respective data value in the enhanced 3-D volume data set when the data value is not within the data value range. The resulting image is an enhanced 3-D volume data set comprising a combination of the original enhanced 3-D volume data set data values, the preselected data values and/or the another preselected data values. In either technique, the image may be further enhanced by the application of an autopicking technique that utilizes an initial seed pick to autopick all connected data values having the same data value as the seed pick. This technique is particularly useful for determining the extent of an event related to a physical phenomenon.
The '781 application describes another technique for corendering multiple attributes in real time thus, forming a combined image of the attributes. The combined image is visually intuitive in that it distinguishes certain features of an object that are otherwise substantially indistinguishable in their natural environment.
Another technique used to analyze certain geological events, like faults and other formation anomalies, is illustrated in U.S. patent application Ser. No. 09/936,682 assigned to Magic Earth, Inc. and incorporated herein by reference. The '682 application describes a technique for imaging and/or tracking a physical phenomena, such as a geological fault, by selecting control points from various locations corresponding to a 3-D data volume set to define a first spline curve and a second spline curve. A surface may be interpolated between the first spline curve and the second spline curve that is representative of the physical phenomena. This technique may also be used to define other surfaces and boundaries of geological formations.
Another technique used to analyze similar geological events is illustrated in U.S. patent application Ser. No. 09/119,635 assigned to Magic Earth, Inc. and incorporated herein by reference. The '635 application describes a technique for imaging and manipulating the image of a 3-D sampling probe, in real time, that is a subset of a larger 3-D volume data set. As the 3-D sampling probe moves through the larger 3-D volume data set, the imaging on the surfaces of the 3-D sampling probe is redrawn “on the fly” so that the image is perceived to change in real time with movement of the 3-D sampling probe thus, enabling a more intuitive analysis of the geological events represented by the 3-D volume data set.
The techniques thus described may be used to locate an image certain attributes representative of geological events like gas-producing regions found in sand and sandstone. Gas-producing regions, however, may be difficult to distinguish from other geological regions comprising limestone and dolomite. In other words, attributes representing gas-producing sands may be masked or otherwise obscured by attributes representing limestone or dolomite. Therefore, there is a need to effectively locate and distinguish attributes representing gas-producing sands from other related geological regions comprising limestone and dolomite.